Superwide band wave absorber

ABSTRACT

A wave absorber composed of a wave-absorbing ferrite wall in combination with a zigzag wave-absorbing dielectric wall disposed on the front side of the ferrite wall which can absorb superwide band waves wherein frequencies between the range of about 100 MHz. and 1,000 MHz. are absorbed by the ferrite wall and frequencies greater than 1,000 MHz. are absorbed by the dielectric wall. The aforementioned abstract is neither intended to define the invention of the application which, of course, is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.

United States Patent Inventor Kunihiro Suetake No. 10-1 1 Minami, 3-Chome, Meguro-Ku, Tokyo, Japan Appl. No. 885,870

Filed Dec. 17, 1969 Patented Nov. 23, 1971 SUPERWIDE BAND WAVE ABSORBER Primary ExaminerMalcolm F. Hubler Attorney-Leonard H. King ABSTRACT: A wave absorber composed of a wave-absorbing ferrite wall in combination with a zigzag wave-absorbing dielectric wall disposed on the front side of the ferrite wall which can absorb superwide band waves wherein frequencies between the range of about 100 MHz. and 1,000 MHz. are absorbed by the ferrite wall and frequencies greater than 1,000 M Hz. are absorbed by the dielectric wall.

The aforementioned abstract is neither intended to define the invention of the application which, of course, is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.

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3 INVENTOR Kum'h'ro Mela/9e ATTORNEY BACKGROUND OF THE INVENTION In the testing of antennas, waveguides and circuit elements used for high-frequency devices, it is necessary to transmit the high-frequency signals in a nonreflecting environment. Since it is often not possible to test the devices in free space, nonreflecting room equivalents to free space have been developed. The rooms are generally coated with a wave absorber to eliminate reflecting of the waves off the solid room structure.

With the development of color television and space programs, antennas and circuit elements must now be designed for wide band applications where the lowest frequency is in the order of 100 MHz. and the highest frequency is more than 1,000 MHz. To test these devices, the wave-absorbing material in the nonreflecting rooms must be capable of extending over this wide band range.

Conventional wave absorbers use dielectric material in varying thicknesses with a metal backing plate. The most efficient type of absorbing wall has been found to be a zigzag type construction of dielectric material where the thicknessv required is equal to 0.8 to 1.2 times the lowest effective wavelength. Accordingly, in order to absorb a wave whose frequency is 1,000 MI-Iz., whose wavelength is equal to 30 cm., the thicknes of the zigzag wall must be about 30 cm. or about 12 inches, while for a frequency of 100 MHz., the thickness must be about 300 cm. or about 120 inches feet). Although other materials have been used to form the wave-absorber wall, their material generally absorb waves of narrow bandwidth and are ineffective for wide bandwidth applications.

According to the present invention a thin sheet of ferrite plate of about 8 to 10 mm. or 0.3 to 0.4 inches is combined with a zigzag dielectric material of about 30 cm. or l2 inches to form an absorber wall capable of absorbing waves over a superwide band frequency range.

It is therefore an object of this invention to provide a waveabsorbing wall for a nonreflecting room meeting the abovementioned requirements.

Another object of this invention is to provide a superwide band absorber which is thin for economic and practical purposes.

Still another object of this invention is to provide a'superwide band absorber by combining a wave absorbing ferrite plate and a zigzag wave-absorbing wall.

A still further object of this invention is to provide a wave absorber which is capable of absorbing frequencies from I00 MHz. to over l,000 MHz. I

Yet another object is to provide a wave absorber of the zigzag type whose thickness is about half of that generally required for wide band frequency waves.

DESCRIPTION OF THE DRAWING This invention is described in greater detail in the following description when read in conjunction with the drawings in which:

characteristic of a zigzag wave-absorbing wall of a dielectric material;

FIG. 4 is a graph of the reflection coefficient-frequency characteristic of a superwide band wave absorbing wall according to this invention.

Referring to FIG. 1, a wall absorber I0 is shown consisting of the dielectric absorber I3 and a thin ferrite plate 12 backed with a very thin metal plate 11. The ferrite plate 12 is of a thickness of about 8 mm or 0.3 inches. Disposed on the front side of the ferrite plate is a dielectric absorber 13 in the form of a zigzag as is commonly known in the art. The zigzag portion of the entire absorber is about 30.8 cm. or about l2 inches in thickness.

FIG. 2 shows the graph of the reflection coefficient of the ferrite plate as a function of frequency. The graph indicates that for very low and high frequencies the coefficient is relatively high, indicating a poor absorption characteristic. How ever, for a narrow range of frequencies, the reflection coefficient is relatively low. If the allowable coefficient of reflection is 0.1, then the effective range of the ferrite plate is from I00 MHz. to about 1,000 MHz.

FIG. 3 shows a similar graph of reflection coefficient against frequency for a zigzag wave absorber of dielectric material having a thickness of about 30 cm. or 12 inches. As can be seen, below 1,000 MHz. the reflection coefficient is above the allowable value of 0.l. Thus, the effective range isgreater than 1,000 MHz.

In order to extend the effective range of the zigzag wall, it was common practice to increase the thickness of the dielectric wall, such that for a thickness of about l0 feet the effective range would be extended downward to about I00 Ml-lz.

In accordance with this invention, as shown in FIG. 1, the ferrite plate and the zigzag dielectric material are combined wherein the wide band absorbing characteristic is obtained as shown in FIG. 4. The plot of the combination of materials as shown in FIG. 4 indicates that the effective range has been extended to I00 MHz. and yet has a reflection coefiicient of less than 0.1 for frequencies greatly in excess of L000 MHz.

The zigzag wall of the prior art is generally composed of a dielectric material containing a graphite composition and for a frequency of MHz. to over l,000 MHz. is about 2.0 to 3.0 meters or 7 to ID feet in thickness. A metal plate is generally arranged on the backside of the dielectric. The absorbing wall of this invention utilizes about 10 percent to 15 percent of the thickness of the same dielectric material containing the graphite composition. A thin ferrite plate is substituted for the major part of lossy dielectric material containing the large amount of the graphite composition. Despite the thinner body, the frequency band over which the wall is effective isnot affected.

What I claim as new and desire to secure by Letters Patent is:

l. A superwide band wave absorber comprising a wave-absorbing wall composed of a ferrite plate and a zigzag wave-absorbing wall disposed in the front of said ferrite plate.

2. A superwide band wave absorber as in claim 1 wherein the allowable reflective coefiicient of the wave absorber is less than 0.1 and the frequency band begins at 100 MHz. and extends to over 1,000 MHz.

3. A superwide band wave absorber as in claim I wherein said ferrite plate is about 0.3 inches in thickness and said zigzag wave-absorbing wall is about 12 inches in thickness.

4. A wave absorber as in claim I wherein said zigzag waveabsorbing wall is of a dielectric niaterial including a graphite composition.

5. A nonreflecting room for use in electromagnetic waves wherein the walls are coated with wave absorbers, said wave absorber comprising a ferrite plate of about 0.3 inches thickness and a zigzag dielectric wall of about 12 inches thick disposed in front of said ferrite plate.

I '0! i l 

1. A super-wide band wave absorber comprising a wave-absorbing wall composed of a ferrite plate and a zig-zag wave-absorbing wall disposed in the front of said ferrite plate.
 2. A super-wide band wave absorber as in claim 1 wherein thE allowable reflective coefficient of the wave absorber is less than 0.1 and the frequency band begins at 100 MHz. and extends to over 1,000 MHz.
 3. A super-wide band wave absorber as in claim 1 wherein said ferrite plate is about 0.3 inches in thickness and said zig-zag wave-absorbing wall is about 12 inches in thickness.
 4. A wave absorber as in claim 1 wherein said zig-zag wave-absorbing wall is of a dielectric material including a graphite composition.
 5. A nonreflecting room for use in electromagnetic waves wherein the walls are coated with wave absorbers, said wave absorber comprising a ferrite plate of about 0.3 inches thickness and a zig-zag dielectric wall of about 12 inches thick disposed in front of said ferrite plate. 